Action server

#ros2   #python   #action  

---

Table of Content

Action server

Create action server that use Counter.action custom message declare at custom_interfaces

Action server create 3 service and 2 topics

Action topics and services

use --include-hidden-topics arg

ros2 topic list --include-hidden-topics 
#
/action_demo/_action/feedback
/action_demo/_action/status
/parameter_events
/rosout

use include-hidden-services on service list

ros2 service  list --include-hidden-services 
/action_demo/_action/cancel_goal
/action_demo/_action/get_result
/action_demo/_action/send_goal

---

Action sequence

Code time

VSCode action intellisense

Add path to search to python.analysis.extraPaths list in settings.json

{
"python.analysis.extraPaths": [
    "/home/user/ros2_ws/install/action_tutorial_interfaces/local/lib/python3.10/dist-packages"
    ]
}

demo

action_tutorial/my_server.py

import rclpy
from rclpy.action import ActionServer
from rclpy.action.server import ServerGoalHandle
from rclpy.node import Node

from custom_interfaces.action import Counter  # pylint: disable=E0401

TOPIC = "my_action_demo"


class MyNode(Node):
    def __init__(self):
        node_name = "action_server"
        super().__init__(node_name)
        self._action_server = ActionServer(self, Counter, TOPIC, self.execute_callback)
        self.get_logger().info("Hello ROS2")

    def execute_callback(self, goal_handle: ServerGoalHandle):
        feedback_msg = Counter.Feedback()
        for i in range(goal_handle.request.count):
            self.get_logger().info(f"current: {i}")
            feedback_msg.current = i
            goal_handle.publish_feedback(feedback_msg)

        self.get_logger().info("Action ended")
        goal_handle.succeed()

        result = Counter.Result()
        result.total = i
        return result


def main(args=None):
    rclpy.init(args=args)
    node = MyNode()
    try:
        rclpy.spin(node)
    except KeyboardInterrupt:
        print("User exit")
    finally:
        node.destroy_node()
        rclpy.try_shutdown()


if __name__ == "__main__":
    main()

package.xml

<!-- Add dependency to custom_interfaces package -->
<depend>custom_interfaces</depend>

Test

Use ROS cli to run action

ros2 interface show custom_interfaces/action/Counter 
int32 count
---
int32 total
---
int32 current

check for actions

ros2 action list
#
/my_action_demo

ros2 action send_goal -f <action_topic> <action messegae> <request part>

ros2 action send_goal -f /my_action_demo custom_interfaces/action/Counter "{count: 5}"

feedback

-f show feedback from server

send_goal

ros2 action send_goal -f /my_action_demo custom_interfaces/action/Counter "{count: 5}"
#
Waiting for an action server to become available...
Sending goal:
     count: 5

Goal accepted with ID: c1129edf0f894012921b849b7948703a

Feedback:
    current: 0

Feedback:
    current: 1

Feedback:
    current: 2

Feedback:
    current: 3

Feedback:
    current: 4

Result:
    total: 4

Goal finished with status: SUCCEEDED

---

Goal States

• ACCEPTED (1): The goal has been accepted and wait for execute.
• EXECUTING (2): The goal is currently running by action server
• CANCELING (3): The client request the server to cancel current goal (cancel accepted)
• SUCCEEDED (4): The goal was successfully by the action server
• CANCELED (5): The goal canceled by the client or external event
• ABORTED (6): The goal terminated by the action server

action server state service

• send_goal: New goal request send to the server, if accepted start the server state machine
• cancel_goal: Request server to stop processing current goal.